Peroxygen bleaching agents have been known for many years and are used in a variety of industrial and domestic bleaching and cleaning processes. The activity of such agents is, however, extremely temperature-dependent, and drops off sharply at temperatures below 60.degree. C. Especially for cleaning fabrics, high temperature operation is both economically undesirable and practically disadvantageous.
One approach to solving this problem has been through the additional use of so-called bleach activators, also known as bleach precursors. These activators typically are carboxylic acid esters that react with hydrogen peroxide anions in aqueous liquor to generate the corresponding peroxyacid which, in turn, oxidises the substrate. However, these activators are not catalytic. Once the activator has been perhydrolysed, it can no longer be recycled and, therefore, it is usually necessary to use relatively high levels of activator. Since bleach activators are relatively expensive, the cost of using activators at such levels may be prohibitive.
Another approach has been to use transition metal complexes as catalysts to activate the peroxy bleaching agent. For example, U.S. Pat. No. 4,728,455 discloses the use of manganese(III)-gluconate as a peroxide bleach catalyst with high hydrolytic and oxidative stability. In EP-A-0,458,379, for example, triazacyclononane-based manganese complexes are disclosed that display a high catalytic oxidation activity at low temperatures, which is particularly suitable for bleaching purposes.
In WO-A-9534628, it has been shown that the use of iron complexes containing certain pentadentate nitrogen-containing ligands, in particular N,N-bis(pyridin-2-ylmethyl)bis(pyridin-2-yl)methylamine ("N.sub.4 Py"), as bleaching and oxidation catalysts, resulted in favourable bleaching and oxidation activity. However, the synthesis of this ligand is relatively costly.
WO-A-9718035 discloses iron and manganese complexes containing ligands such as N,N'-bis(pyridin-2-ylmethyl)ethylene-1,2-diamine ("Bispicen"), N-methyl-N,N',N'-tris(pyridin-2-ylmethyl)ethylene-1,2-diamine ("TrispicMeen"), and N,N,N',N'-tetrakis(pyridin-2-ylmethyl)ethylene-1,2-diamine ("TPEN"), as peroxide oxidation catalysts for organic substrates.
WO-A-9748787 relates to iron complexes having polydentate ligands containing at least six nitrogen or oxygen hetero atoms, the metal ion being coordinated by at least five hetero atoms, for example 1,1,4,8,11,11-hexa(pyridin-2-ylmethyl)-1,4,8,11-tetra-aza-undecane ("Hptu"), as catalysts for peroxide, peroxyacid and molecular oxygen bleaching and oxidation.
Whilst known transition metal complexes have to an extent been used successfully as catalysts in bleaching or oxidation processes, there remains a need for other bleaching and oxidation catalysts, preferably that are more effective in terms of activity or cost.
We have now surprisingly found that a significant or improved catalytic activity can be achieved by an iron, manganese or copper complex having a pentadentate ligand comprising substituted heteroaryl groups. Furthermore, we have found that catalysts exhibiting such activity can be produced by easily accessible syntheses.